Many methods and devices have already been disclosed to that end.
U.S. Pat. No. 5,626,651 describes a method and a system of this type according to which the turbulent gaseous stream flows above a series of plates which define non-turbulent zones in which the particles are trapped. More precisely, the plates are parallel to one another and vertical. A filtering means consisting of fibers can also be provided between said plates in order to improve filtration of the finer particles notably.
International patent application WO-95/28,217 describes a device based on the same principle, but where the plates are provided with slots or replaced by grates.
Furthermore, patent application WO-97/00,102 relates to a separator arranged at the exhaust of Diesel type engines in order to collect the particles contained in the exhaust gas.
A honeycomb structure is therefore pierced with channels perpendicular to the opening of the honeycomb cells, this structure having a porosity of the order of 70%.
However, it has been observed that this type of separator cannot be used for fogs because the droplets trapped in the material cannot be removed by drainage.
International patent application WO-97/27,928 relates to a separator provided with one or more vertical flow channels laterally delimited by fibrous corrugated elements.
In this document, an agglomerator is necessarily arranged upstream from the separator in order to have larger particles likely to be separated in the separator. This is therefore relatively expensive and involves pressure drops that are by no means insignificant.
In U.S. Pat. No. 5,626,651, the trapped particles accumulate on the walls, then fall under the effect of gravity onto the bottom of the device. Means intended to shake the walls are often required to cause these particles accumulated on the walls to fall down.
This device poses problems when very fine particles, smaller than one micrometer, are to be separated. In this case, the height of the flow channel must be very small and therefore the height of the plates very large so that the equipment is quite bulky for a very small section of flow. The same problem exists in the device according to document WO-95/28,217.
However, these known means do not allow to collect and to remove efficiently particles in liquid or solid form whose size is less than about one micrometer.
Patent application WO-99/19,044 published in the name of the applicant describes a separator made of a foam comprising channels intended for the turbulent flow of the gaseous effluents, which allows to overcome the aforementioned drawbacks.
However, the applicant has continued research in the sphere of separation and has been able to develop a device which significantly improves the separation of very small particles present in gaseous effluents.
In a first research stage, it has been observed that, when a gaseous effluent in the turbulent state containing suspended particles flows through a channel 2 of diameter D made from a porous material (see FIG. 1), the boundary layer of this effluent enters, from the peripheral edge delimiting this channel, the inside of the porous material over a thickness L of a peripheral stratum 3 and, as a result of the eddy generated by this effluent, the particles are carried into this stratum 3 where they are collected by the fibers of the pores of the porous material.
Channel 2 therefore remains free of any hindrance, which allows the gaseous effluent to flow all along the channel with a constant pressure drop and flow rate since the accumulation of the particles collected lies in an annular space surrounding this channel.
According to the same principle and during another research stage, it has been discovered that, when a gaseous effluent in the turbulent state containing suspended particles flows along a face of a porous material in form of a sheet, the boundary layer of this effluent moves towards the inside of the porous material and, by means of the turbulent eddy generated by this effluent, the particles are carried into the superficial layer of this sheet where they are collected by the fibers of the pores of the porous material.
Similarly, in this configuration, the pressure drop of the effluent is minimal since the particles have accumulated in the body of the sheet without hindering the flow of this effluent.